Hitherto, processing size has been becoming finer in lithography to obtain a higher integration degree in the field of fine processing technique, a typical example of which is the production of integrated circuit elements. Lithographic technique has been recently required which is capable of attaining fine processing at a level of about 200 nm or less, using an ArF excimer laser (wavelength: 193 nm), a F2 excimer laser (wavelength: 157 nm) and the like. As a resist suitable for irradiation with such an excimer laser, suggested are many resists making use of chemically amplifying effect (hereinafter referred to as “chemically amplification type resist”) based on a component having an acid-disassociating functional group and a component which is subjected to irradiation with a radiation (hereinafter referred to as “exposure”) so as to generate an acid (hereinafter referred to as “acid generator”). Regarding the chemically amplification type resist, a resist comprising a resin having a t-butyl ester group of a carboxylic acid or a t-butyl carbonate group of phenol, and an acid generator is suggested. This resist makes use of the following phenomenon: an acid generated by exposure functions so as to dissociate the t-butyl ester group or t-butyl carbonate group present in the resin, and thus the resin comes to have an acid group that is a carboxyl group or a phenolic hydroxyl group so that an exposed area of the photoresist film turns easily-soluble in an alkaline developer.
In such lithography, the formation of a finer pattern is required for the future. Investigations on fine processing using an ArF excimer laser (wavelength: 193 nm) are particularly becoming active.
A radiation used ordinarily in lithographic process is a single-wavelength ray, thus an incident radiation and a reflected radiation on the upper and lower interfaces of a photoresist film interfere with each other in the photoresist film. As a result, a phenomenon called “standing wave effect” or “multi-interferential effect”, that is, a phenomenon that even when the dose of exposure is constant, a fluctuation in the thickness of the photoresist film causes a fluctuation in effective exposure dose to the photoresist film on the basis of mutual interfere between the radiations in the film, is generated. This is caused a problem that a bad effect is produced onto the formation of a resist pattern. For example, in the case where the thickness of an applied resist film is varied in accordance with a slight variation of the composition and viscosity of the resist, application conditions of the resist or others, and in the case where the thickness of the resist film applied on the substrate is made uneven due to difference in level of a substrate (the thickness at a concave part becomes larger than that of a convex part), an effective exposure dose to the photoresist film is varied by the film thickness difference, so that the dimension of an obtained pattern fluctuates, or the dimension precision of the resist pattern lowers. Such problems about the standing wave effect become serious particularly in an ion implantation process, wherein a used substrate gives a large reflectivity. Thus, it is desired to overcome the problems.
In order to solve the problems about the standing wave effect, a method has been hitherto suggested wherein an upper antireflective film is formed on a photoresist film to restrain reflection on the surface of the photoresist film and reduce multi-interfere in the film. For example, Non-patent document 1 discloses a technique in which an upper antireflective film comprising a polysiloxane, a polyethylvinylether, a polyvinylalcohol or the like is laminated on a photoresist film to reduce the standing wave effect. It is described that: in this case, the reflection-restraining effect on the photoresist film surface depends mainly on the refractive index and the thickness of the antireflective film; the refractive index of the upper antireflective film is ideally √n wherein n is the refractive index of the resist, and the thickness of the upper antireflective film is ideally an odd multiple of λ/4 m wherein λ is the wavelength of a radiation, and m is the refractive index of the upper antireflective film.
[Non-Patent Document 1] J. Electrochem. Soc., Vol. 137, No. 12, P. 3900 (1990)
The refractive index of a resists is generally in the range from 1.6 to 1.8. Therefore, an upper antireflective film having a refractive index of 1.4 or less is required in order to restrain the standing wave effect sufficiently. The refractive index of an upper antireflective film comprising a polysiloxane, a polyethylvinylether or a polyvinyl alcohol is generally 1.5 or more, however, the standing wave effect cannot be sufficiently restrained. When the processing size becomes finer in lithography so that the control of the line width of a pattern is stricter in the future, an upper antireflective film having a smaller refractive index will become necessary.
Additionally, an upper antireflective film is required to have a high transmittance as well as a small refractive index. This is because: when an upper antireflective film has an intensely absorptive band, light reaching the resist film becomes weak to cause a problem that the sensitivity is declined so that the throughput falls. It is therefore preferred that the absorption coefficient (k value) of the upper antireflective film is small. It can be mentioned that the absorption coefficient is practically 0.25 or less.
Further, a lithographic process for the production of an integrated circuit element in recent years has a problem of defects generated when a resist film is developed. Examples of the defect include a bridge defect and a scum in line and space patterns, a poor openings defect and a scum in contact hole patterns, and the like. A cause for these defects is that a material hardly soluble in a developer adheres again onto the resist or the substrate at the time of rinsing after development. This defect is called a blob defect.
If the blob defect can be overcome, the yield of an integrated circuit element is improved in production of the element. Thus, many investigations have been made hitherto. However, a method for solving the defect sufficiently has not yet been found out.